1. Field of the Invention.
This invention relates to flashlamp pumped lasers and, more particularly, to circuitry and systems for controlling the pulse width of lasers which are pumped by a flashlamp.
2. Description of the Related Art.
The word "laser" is an acronym for the principal feature of laser action: light amplification by stimulated emission of radiation. There are many different kinds of lasers, but all share a crucial element: each contains material capable of amplifying radiation.
The first construction of a laser is said to have been by T. H. Maiman in 1960. Lasers quickly expanded into various fields of application. There are gas lasers and solid state lasers. Some are operative in a continuous mode; others are operated in a pulsed mode which may permit the laser to emit tremendous levels of peak power for extremely short intervals.
The principal reason for utilization of lasers is their property of being able to emit coherent light radiation, which means that an extremely narrow beam can be transmitted for long distances without degradation of the phase relationships and with very limited dispersion. The ability of the laser to direct concentrated energy at precisely located targets and in precisely measured amounts also makes the laser useful in surgical applications, welding, etc. The coherent property of the light radiation has made possible the development of the technology of holography. There are many other uses of lasers, both industrial and scientific.
According to the literature, the first laser was pumped with the bright flash of light from a Xenon flashlamp, and flashlamp pumping remains common today (see the book entitled "SOLID-STATE LASERS" by Jeff Hecht, copyright 1988, Howard Sams & Co. (page 237 et seq).
Known existing laser systems which have the capability of varying laser pulse width are very large and expensive. These systems use very large power supplies to charge storage capacitors at a very rapid rate in order that the laser can be fired again within a short time after the previous pulse. In systems of this type, laser pulses are controlled by a device known as a Q-switch. Such devices enable the generation of very short (approximately 30 nanosecond), intense laser pulses by enhancing the storage and dumping of electronic energy in and out of the lasing medium. A Q-switch may, for example, be used with a ruby laser in a dual-pulse mode for holographic measurements. In such a mode, a Q-switch generates two short pulses during a single long flashlamp pulse, thus turning the laser on twice during the millisecond duration of the flashlamp pulse. This kind of operation has limited application and the required control equipment is cumbersome and costly.
Other lasers, such as those used to set off pyrotechnic devices--e.g., explosive bolts and the like--are generally much smaller capacity, single shot units which have no control of pulse width nor any capability of firing laser pulses in rapid succession.
In pyrotechnic systems such as are known, there is either one laser per ordnance device or there must be a substantial waiting time between the firing of successive laser pulses. This interval is on the order of hundreds of milliseconds. In systems where it is desirable to generate laser pulses in rapid succession, the power supplies are necessarily very large and expensive, as noted above. In some laser systems, such as those which are used in a laboratory, it is desirable to be able to control the pulse width with control equipment of much less cost and complexity.